1. Field of the Invention
This invention relates to a power supply for electro-erosion machine, in particular to an electro-erosion power supply comprising a low resistance circuitry, used in die sinker Electrical Discharge Machine (EDM), hole drilling EDM, wire EDM or other equipment using electro-erosion process to cut the work-piece.
2. Description of the Related Prior Art
The EDM has an electrical discharge power supply connected to the gap formed by the electrode and the work-piece, for providing a machining current through the gap to cut the work-piece. In order to avoid arcing and to get the desire surface roughness on the work-piece, the amplitude of the gap current need to be controlled or limited during a single pulse (ON TIME), and an ON-OFF time signal is also used to start/stop the gap current during cutting the work-piece.
FIG. 14 has shown a prior art, which is an early prior art to control and limit the gap current, that utilizes a resistor connected in series to the gap to limit the current, however, the current flow through the gap also through the resistor, thus causes huge power loose. Further, although the resistors limit the current to a certain valve, the gap current may still change while the gap condition has been changed.
Later, a U.S. Patent was issued with U.S. Pat. No. 5,534,675, as shown in FIG. 15, which did not use serial resistors to limit the gap current, in stead, it uses a switching element being connected in series in the current loop and a current feedback resistor to detect the current flow through the gap, By switching the switching device on and off it limit the gap current. Because of no passive component to limit the current, it may cause serious damage when the switching device, the driving circuit of switching elements or the current detection circuit malfunction, the current will be out of control and causes circuit damages. Further, due to the high frequency operation and high current switching stress of switching element, the switching element must have big heat sink; and may also causes big electromagnetic noise. Although the prior art shown in FIG. 15 is compact with respect to the FIG. 14, however, the prior art in FIG. 15 still has safety concern for its lacking of passive component connected in series in the current loop to limit the gap current.
It is the primary object of the present invention to provide a low resistance power supply for electro-erosion machine, which comprises a capacitive network in series connected in the current loop to limit the current at the gap formed by the electrode and work-piece, a switching device is adapted to change the direction of charging or discharging current of said capacitive network to continually pass the current, and a driving circuit to turn the switching device ON and OFF repeatedly during ON time, so as to control the gap current. Owing to the character of the capacitive network, this design is a safe low resistant power supply circuitry, which eliminates a high power loose and reduces the switching stress on the switching device.
The electro-erosion ON-OFF time signal and current pattern control is connected to this circuitry forming a compact, low power loose and low electromagnetic noise electro-erosion power supply.